The present invention relates to a moisture-proof container of solid, moisture-curable composition for use as a hot-melt as described in our U.S. Pat. No. 4,586,636.
Since moisture-curable compositions are cured by reaction with moisture, it is necessary to inhibit exposure of these compositions to moisture prior to use, and yet to provide for emptying of the container, even only partially, without premature cure of the composition.
Our U.S. patent specification No. 4,586,636, describes the use of apparatus for dispensing a moisture-curable composition provided in a self-supporting package comprising a container having a tubular body portion closed at one end by a closure member provided with an outlet, said container further comprising within the body portion a slideable piston-head so that the composition is confined in the body portion between the piston-head and the closure member, the apparatus comprising exit port means adapted to cooperate with the outlet of the package so as to provide a moisture-proof seal between the outlet and the exit port means, actuating means for pressing the piston-head towards the closure member and the outlet, and means for conducting molten composition from the exit port means to a dispenser nozzle without exposing the composition to atmospheric moisture, characterised in that the composition contained in the package is a solid, moisture-curable adhesive to be dispensed as a melt, that the closure member is heat-receptive and cooperates with means for supplying heat to said closure member and in that the slideable piston-head has a rim projecting towards the closure member and in sliding, sealing engagement with an inner wall of said body portion. In operation heat applied to the closure member melts the composition adjacent said closure member and the molten material so formed is expelled through the outlet by movement of the piston head towards the closure member resulting from pressure applied to said piston-head by the actuating means.
Containers made for use in accordance with the above invention are filled when inverted, having the piston-head located at the lower end which is sealed by a lid which is removed before use. The inner walls of the container are provided with a coating of release material such as PTFE. The container is then filled with molten material, sealed at the upper end by the closure member and the container is then inverted and allowed to cool. With compositions which are crystalline at room temperature, shrinkage on solidification provides a small gap between the walls of the container and the mass of solid composition. When the container is used, the small gap facilitates the passage of the projecting rim of the piston-head when in sliding engagement with the inner wall of the container.
However, difficulties are experienced with noncrystalline compositions which do not shrink to provide the small gap which facilitates the passage of the projecting rim in use and operation of the dispensing apparatus is hindered.
It is one object of the present invention to provide an improved container for use in dispensing a hot-melt using apparatus described in U.S. Pat. No. 4,586,636 which is easily usable with a non-crystalline composition.
Difficulties are also experienced with larger containers filled with crystalline composition since the mass of the composition can produce irregular shrinkage which produces voids which permit the entry of molten material when the apparatus is used and this backflow of molten material may even pass the seal provided by the projecting rim of the piston-head engaging the inner wall of the container.
It is accordingly a further object of the present invention to provide an improved container for use in the apparatus described in European patent specification 0102804 which obviates the backflow of molten materials against the projecting rim of the piston-head.